The invention relates to oil metering pumps, including those supplying oil to a two-cycle internal combustion engine in metered amounts.
The invention arose during efforts developing an oil metering pump for a marine outboard drive unit having a two-cycle internal combustion engine. In various of such units, it is desirable to provide an automatic oil-fuel mixing system, eliminating the need to manually pre-mix the oil and fuel. The automatic system draws oil from an oil tank and fuel from a fuel tank, and mixes the oil and fuel in a desired ratio. In other applications, it is desirable to provide oil injection.
In a marine outboard drive unit, space is at a premium. It is desirable to locate an oil storage tank on the drive unit, however not at the expense of enlarging the cowl which houses the engine at the top of the. driveshaft housing. In copending application Ser. No. 07/360,273, filed June 2, 1989, entitled "Marine Outboard Drive With Oil Tank", an oil tank is desirably mounted at a location beneath the cowl and around the driveshaft housing. This location makes use of existing space, without interferring with operation of the unit. This also eliminates redesign problems of mounting an oil tank within the cowl, and enlarged cowl dimensions otherwise required thereby. The present invention is particularly useful in combination with the oil tank of the noted copending application.
In the preferred embodiment of the present invention, the oil pump is located within the cowl and above the oil tank. This in turn requires that the oil pump be able to draw oil upwardly from the oil tank. The present oil pump is designed to operate with the oil tank mounted at a location lower than the oil pump so that the oil pump is required to lift the oil to the suction or supply input of the oil pump. However, the pump may also be operated from a position below the tank.
Various metering oil pumps are known in the prior art, however they are not recommended to operate with the oil tank mounted below the oil pump. While such prior pumps are capable of lifting the oil, such orientation is not recommended because of the possibility of air entry. If an air bubble should get into the oil supply input to the pump, the pump will not deliver oil to the engine while the bubble is being purged.
Prior pumps typically have an air bleed screw in the pump body. It is necessary to bleed the air from the line by loosening this screw when the system is being assembled or serviced. Some prior pumps have an air vent which may be returned to the oil tank. The pumps are mounted below the oil tank, so that after assembly, no air enters the pump, and hence there is no chance of an air bubble being delivered to the engine in place of oil.
The present invention provides an oil pump which can be mounted above the oil tank. The oil pump includes a positive air purging stroke which displaces air and removes same from the oil.
The invention is particularly useful in combination with, the oil tank of above noted copending application Ser. No. 07/360,273, filed June 2, 1989, entitled "Marine Outboard Drive With Oil Tank", and with the fill tube of copending application Ser. No. 07/360,272, filed June 2, 1989, entitled "Marine Outboard Drive With Oil Tank Fill Tube", and with the draw tube and indicator assembly of copending application 07/360,272, filed June 2, 1989, entitled "Marine Outboard Drive With Oil Tank Draw Tube and Indicator".